Optical Multilayer Structure and Method of Manufacturing the Same

ABSTRACT

An optical multilayer structure including: a substrate; a shatterproof layer which is formed on at least one surface of the substrate and includes a polyimide film including a polyimide precursor, a polyimide, or a combination thereof including a structure of the following Chemical Formula 1, and inorganic particles; and a hard coating layer formed on the other surface of the substrate: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 1  and R 2  are independently of each other C 1-5  alkyl which is unsubstituted or substituted with one or more halogens; R 3  and R 4  are independently of each other C 6-10  aryl which is unsubstituted or substituted with one or more halogens; L 1  and L 2  are independently of each other C 1-10  alkylene; and x and y are independently of each other an integer of 1 or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No.10-2022-0063876, filed May 25, 2022, Korean Patent Application No.10-2022-0063866, filed May 25, 2022, and Korean Patent Application No.10-2023-0054300, filed Apr. 25, 2023, the disclosures of each of whichare hereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The following disclosure relates to an optical multilayer structure anda method of manufacturing the same.

Description of Related Art

A polyimide film is a material for a substrate, a cover window, and thelike of a display device, and is attracting attention as anext-generation material which may replace tempered glass. In order toapply a film to a display device, it is essential to improve intrinsicyellow index characteristics and impart colorless and transparentcharacteristics, and furthermore, in order to make the film applicableto a foldable or flexible display device, mechanical properties shouldbe also improved, and thus, the required performance of the polyimidefilm for a display device is gradually increased.

In particular, it is important to design a flexible display device whichmay be bent or folded when the user wants as a flexible structure sothat the device is not easily broken upon external impact or during abending or folding process.

SUMMARY OF THE INVENTION

An embodiment of the present disclosure is directed to providing amultilayer structure comprising: a structure comprising a polyimideshatterproof layer having a relaxed thermal expansion-shrinkage behaviorformed on one surface of a substrate and a hard coating layer formed onthe other surface of the substrate; or

-   -   a structure in which the shatterproof layers are formed on both        surfaces of the substrate, wherein curling is excellently        improved and surface hardness is significantly increased.

Another embodiment of the present disclosure is directed to providing amethod of manufacturing the optical multilayer structure.

Still another embodiment of the present disclosure is directed toproviding a window cover film comprising the optical multilayerstructure and a flexible display panel comprising the same.

In one general aspect, an optical multilayer structure comprises:

-   -   a substrate;    -   a shatterproof layer which is formed on one surface of the        substrate and comprises a polyimide film comprising a polyimide        precursor, a polyimide, or a combination thereof comprising a        structure of the following Chemical Formula 1, and inorganic        particles; and    -   a hard coating layer formed on the other surface of the        substrate:

-   -   wherein    -   R⁴ and R² are independently of each other C₁₋₅ alkyl which is        unsubstituted or substituted with one or more halogens;    -   R³ and R⁴ are independently of each other C₆₋₁₀ aryl which is        unsubstituted or substituted with one or more halogens;    -   L⁴ and L² are independently of each other C₁₋₁₀ alkylene; and    -   x and y are independently of each other an integer of 1 or more.

In one embodiment, the optical multilayer structure may further comprisea shatterproof layer between the substrate and the hard coating layer.

In another general aspect, a method of manufacturing the opticalmultilayer structure according to the implementation comprises: applyinga polyimide precursor composition on one surface of a substrate anddrying the composition to form a shatterproof layer; and applying acomposition for forming a hard coating layer on the other surface of thesubstrate and curing the composition to form a hard coating layer.

In another general aspect, a method of manufacturing the opticalmultilayer structure according to the implementation comprises: applyinga polyimide precursor composition on both surfaces of a substrate (theone surface of the substrate and the other surface of the substrate) anddrying the composition to form a first shatterproof layer on the onesurface of the substrate and a second shatterproof layer on the othersurface of the substrate; and applying a composition for forming a hardcoating layer on any one of the first shatterproof layer or the secondshatterproof layer formed on the substrate and curing the composition toform a hard coating layer.

In another general aspect, a window cover film comprises the opticalmultilayer structure according to the implementation.

In still another general aspect, a flexible display panel comprises thewindow cover film according to the implementation.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 schematically show a structure of an optical multilayerstructure according to one implementation.

Detailed Description of Main Elements

-   -   100: Optical multilayer structure    -   10: Display element    -   20: Substrate    -   30: Shatterproof layer    -   40: Hard coating layer

DESCRIPTION OF THE INVENTION

The embodiments described in the present specification may be modifiedin many different forms, and the technology according to one embodimentis not limited to the embodiments set forth herein. Furthermore,throughout the specification, unless explicitly described to thecontrary, “comprising” any constituent elements will be understood toimply further inclusion of other constituent elements.

The numerical range used in the present specification comprises allvalues within the range comprising the lower limit and the upper limit,increments logically derived in a form and spanning in a defined range,all double limited values, and all possible combinations of the upperlimit and the lower limit in the numerical range defined in differentforms. As an example, when it is defined that a content of a compositionis 10% to 80% or 20% to 50%, it should be interpreted that a numericalrange of 10% to 50% or 50% to 80% is also described in the specificationof the present. Unless otherwise defined in the present specification,values which may be outside a numerical range due to experimental erroror rounding of a value are also comprised in the defined numericalrange.

Hereinafter, unless otherwise particularly defined in the presentspecification, “about” may be considered as a value within 30%, 25%,20%, 15%, 10%, or 5% of a stated value.

Hereinafter, unless otherwise particularly defined in the presentspecification, a “combination thereof” refers to mixing orcopolymerization of constituents.

Hereinafter, unless otherwise particularly defined in the presentspecification, the term “A and/or B” in the present specification mayrefer to an embodiment comprising both A and B or an embodimentselecting one of A or B.

Hereinafter, unless otherwise particularly defined in the presentspecification, a “polymer” may comprise an oligomer and a polymer andmay comprise a homopolymer and a copolymer. The copolymer may comprise arandom copolymer, a block copolymer, a graft copolymer, an alternatingcopolymer, a gradient copolymer, or all of them.

Hereinafter, unless otherwise particularly defined in the presentspecification, a “polyamic acid” refers to a polymer comprising astructural unit comprising an amic acid moiety, and a “polyimide” mayrefer to a polymer comprising a structural unit comprising an imidemoiety.

Hereinafter, unless otherwise particularly defined in the presentspecification, a polyimide film may be a film comprising a polyimide,and specifically, may be a high thermal resistant film manufactured byperforming solution polymerization of an acid anhydride compound in adiamine compound solution to prepare a polyamic acid, and performingimidization.

Hereinafter, unless otherwise defined in the present specification, itwill be understood that when an element such as a layer, a film, a thinfilm, a region, or a substrate is referred to as being “on” or “above”another element, it may be “directly on” the other element orintervening elements may also be present.

Hereinafter, unless otherwise particularly defined in the presentspecification, “substituted” refers to a hydrogen atom in a compoundbeing substituted with a substituent, and for example, the substituentmay be selected from deuterium, halogen atoms (F, Br, Cl, or I), ahydroxyl group, a nitro group, a cyano group, an amino group, an azidogroup, an amidino group, a hydrazino group, a hydrazono group, acarbonyl group, a carbamyl group, a thiol group, an ester group, acarboxyl group or a salt thereof, a sulfonic acid group or a saltthereof, a phosphoric acid or a salt thereof, a C₁₋₃₀ alkyl group, aC₂₋₃₀ alkenyl group, a C₂₋₃₀ alkynyl group, a C₆₋₃₀ aryl group, a C₇₋₃₀arylalkyl group, a C₁₋₃₀ alkoxy group, a C₁₋₂₀ heteroalkyl group, aC₃₋₂₀ heteroarylalkyl group, a C₃₋₃₀ cycloalkyl group, a C₃₋₁₅cycloalkenyl group, a C₆₋₁₅ cycloalkynyl group, a C₂₋₃₀ heterocyclicgroup, and/or a combination thereof.

An ultra-thin tempered glass (ultra thin glass, UTG) is a tempered glassmaterial component used in a display cover window, and a method ofcoating a polyimide film for scattering resistant coating on UTG isknown, but the problem of film curling in a drying step due to adifference in a thermal expansion coefficient between UTG and apolyimide film has not been solved. Meanwhile, a conventional materialfor improving curling has partially improved curling by introducing aflexible structure and the like, but surface hardness was significantlydecreased due to the flexible properties. Thus, in one implementation, astress relaxation segment is introduced into a polyimide precursormolecule, thereby providing a polyimide precursor which may minimizecurling and also minimize a decrease in surface hardness when coated onUTG, and a composition comprising the same.

One implementation provides an optical multilayer structure comprising:

-   -   a substrate;    -   a shatterproof layer which is formed on one surface of the        substrate and comprises a polyimide film comprising a polyimide        precursor, a polyimide, or a combination thereof comprising a        structure of the following Chemical Formula 1 (or a structure        unit comprising the same), and inorganic particles; and    -   a hard coating layer formed on the other surface of the        substrate:

-   -   wherein    -   R¹ and R² are independently of each other C₁₋₅ alkyl which is        unsubstituted or substituted with one or more halogens;    -   R³ and R⁴ are independently of each other C₆₋₁₀ aryl which is        unsubstituted or substituted with one or more halogens;    -   L¹ and L² are independently of each other C₁₋₁₀ alkylene; and    -   x and y are independently of each other an integer of 1 or more.

In one embodiment, R¹ and R² may be independently of each other C₁₋₃alkyl which is unsubstituted or substituted with one or more halogens,C₁₋₂ alkyl which is unsubstituted or substituted with one or morehalogens, or methyl which is unsubstituted or substituted with one ormore halogens. Also, R³ and R⁴ may be independently of each other C₄₋₈aryl which is unsubstituted or substituted with one or more halogens,C₆₋₈ aryl which is unsubstituted or substituted with one or morehalogens, or phenyl which is unsubstituted or substituted with one ormore halogens. Also, L¹ and L² may be independently of each other C₁₋₅alkylene, C₂₋₅ alkylene, or propylene. The alkyl or the aryl substitutedwith one or more halogens may be substituted with one or more halogensselected from I, Br, Cl, and/or F.

In one embodiment, x and y may be independently of each other 1 to 100,1 to 50, 1 to 30, or 1 to 20, but are not necessarily limited thereto.In addition, for example, when the sum of x and y is 100, x may be 1 to99 and y may be 99 to 1, or x may be 10 to and y may be 90 to 10.

In one embodiment, the structure of Chemical Formula 1 comprises or maybe a dimethylsiloxane-diphenylsiloxane (DMS-DPS) structure of thefollowing Chemical Formula 3:

-   -   wherein L¹ and L² are independently of each other C₁₋₁₀        alkylene; and x and y are independently of each other an integer        of 1 or more.

In one embodiment, the polyimide precursor, the polyimide, or thecombination thereof may comprise a unit derived from a diaminecomprising the structure represented by Chemical Formula 1. An exampleof the diamine comprising the structure of Chemical Formula 1 comprisesX-22-1660B-3 available from Shin-etsu having the following structure:

-   -   wherein a and b are independently of each other an integer of 1        or more, 1 to 50, 1 to 30, or 1 to 20, but is not necessarily        limited thereto. Also, for example, when the sum of a and b is        100, a may be 1 to 99 and b may be 99 to 1, or a may be 10 to 90        and b may be 90 to 10.

The polyimide precursor, the polyimide, or the combination thereofcomprises the structure of Chemical Formula 1, thereby minimizingcurling due to a difference in thermal properties between differenttypes of layers when an ultrathin tempered glass is coated with it.

In one embodiment, the shatterproof layer may be formed from a polyimideprecursor composition comprising the polyimide precursor, the polyimide,or the combination thereof, and the inorganic particles.

The polyimide precursor composition may comprise a solvent having anegative distribution coefficient and/or a solvent having a positivedistribution coefficient. An example of the solvent having a negativedistribution coefficient comprises propylene glycol methyl ether (PGME),dimethyl formamide (DMF), dimethyl acetamide (DMAc),N,N-dimethylpropanamide (DMPA), N-ethylpyrrolidone (NEP), and/ormethylpyrrolidone (NMP). In addition, an example of the solvent having apositive distribution coefficient comprises cyclohexanone (CHN),N,N-diethylpropaneamide (DEPA), N,N-diethylacetamide (DEAc), and/orN,N-diethylformamide (DEF).

Without being limited to a certain theory, in one embodiment, thepolyimide precursor composition uses a mixed solvent comprising both thesolvent having a negative distribution coefficient and the solventhaving a positive distribution coefficient, thereby effectivelyimproving curling. Otherwise, in one embodiment, the composition usesboth the solvent having a negative distribution coefficient and thesolvent having a positive distribution coefficient, therebysignificantly increasing the uniformity of the composition (solution) toimprove cloudiness and phase separation, and thus, a colorless andtransparent polyimide film may be manufactured therefrom. In addition,when a substrate is coated with a polyimide film by using both thesolvent having a negative distribution coefficient and the solventhaving a positive distribution coefficient, curling due to a differencein thermal properties between different types of layers may beminimized. However, since the solvent may be differently employeddepending on the monomer of the polyimide precursor, the presentdisclosure is not necessarily limited to a specific solvent or acombination of solvents.

In one embodiment, when the solvent comprised in the polyimide precursorcomposition is a mixed solvent of the solvent having a negativedistribution coefficient and the solvent having a positive distributioncoefficient, a mass ratio between the solvent having a negativedistribution coefficient and the solvent having a positive distributioncoefficient may be 5:5 to 9.5:0.5. Otherwise, the mass ratio may be 5:5to 9:1, 6:4 to 9:1, 6.5:3.5 to 9:1, 7:3 to 9:1, or 7.5:2.5 to 8.5:1.5,but is not necessarily limited thereto.

In one embodiment, the solvent comprised in the polyimide precursorcomposition may comprise at least one, specifically one or more, two ormore, three or more, or 1 to 3 hydroxyl groups (—OH) in the molecule.Otherwise, the solvent may be a solvent comprising any one or more of anether group (—O—) and an oxo group (═O).

In one embodiment, the unit comprising the structure of Chemical Formula1 may be comprised at 20 wt % or more, 25 wt % or more, 30 wt % or more,40 wt % or more, 20 wt % to 70 wt %, 20 wt % to wt %, 25 wt % to 60 wt%, 30 wt % to 55 wt %, or 20 wt % to 50 wt % with respect to the totalweight of the polyimide precursor, but is not necessarily limitedthereto.

In one embodiment, the unit comprising the structure of Chemical Formula1 may be comprised at 30 wt % or more with respect to the total weightof the unit derived from the diamine comprised in the polyimideprecursor. Otherwise, for example, it may be comprised at 40 wt % ormore, 50 wt % or more, 60 wt % or more, 40 wt % to 90 wt %, 40 wt % to80 wt %, or 40 wt % to 60 wt %, but is not necessarily limited thereto.

In one embodiment, the unit comprising the structure of Chemical Formula1 may be comprised at 50 mol % to 99 mol %, 60 mol % to 99 mol %, 70 mol% to 99 mol %, 75 mol % to 99 mol %, 70 mol % to 95 mol %, 80 mol % to95 mol %, 90 mol % to 95 mol %, or about 93 mol %, with respect to thetotal moles of the diamine in the monomer comprised in the polyimideprecursor, but is not necessarily limited thereto.

In one embodiment, the unit comprising the structure of Chemical Formula1 may be a unit derived from an acid anhydride and/or a diaminecomprising the structure of Chemical Formula 1. Herein, the acidanhydride or the diamine may have a molecular weight of 3000 g/mol ormore, 3500 g/mol or more, 4000 g/mol or more, 3000 g/mol to 5500 g/mol,3500 g/mol to 5000 g/mol, or 4000 g/mol to 5500 g/mol, but is notnecessarily limited thereto.

In one embodiment, the polyimide precursor, the polyimide, or thecombination thereof may further comprise a unit derived from a diaminerepresented by the following Chemical Formula 2:

-   -   wherein    -   R¹¹ and R²¹ are independently of each other hydrogen or a C₁₋₂₀        monovalent organic group;

L¹¹ is —SO₂—, —O—, or —C(═O)O—, or a C₁₋₂₀ divalent organic groupcomprising any one or more of these bonds; and

Chemical Formula 2 does not comprise a fluorine atom. In one embodiment,R¹¹ and R²¹ may be independently of each other selected from a C₁₋₁₅monovalent organic group, a C₁₋₁₀ monovalent organic group, a C₁₋₈monovalent organic group, a C₁₋₅ monovalent organic group, or a C₁₋₃monovalent organic group, and for example, the organic group may beselected from alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl,aryl, heteroaryl, oxo (═O), ester, amide, or combinations thereof, butare not necessarily limited thereto.

In one embodiment, L¹¹ may be a C₁₋₁₈ divalent organic group, a C₁₋₁₅divalent organic group, a C₁₋₁₀ divalent organic group, or a C₁₋₆divalent organic group comprising any one or more of —SO₂—, —O—, and—C(═O)O—, or may be a combination of any one or more of —SO₂—, —O—, and—C(═O)O—and C₁₋₁₀ alkyl, C₅₋₁₈ cycloalkylene, and C₆₋₁₈ arylene, but isnot necessarily limited thereto. Also, L¹¹ may be, for example, —SO₂—,—O—, —C(═O)O—,

In addition, L¹¹ may be substituted with a hydroxyl group, a thiolgroup, a nitro group, a cyano group, C₁₋₁₀ alkyl, C₆₋₂₀ aryl, or C₅₋₂₀cycloalkyl. However, L¹¹ does not comprise a fluorine atom bond.

In one embodiment, the diamine represented by Chemical Formula 2 maycomprise or be 4,4′-oxydianiline (ODA),2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4′-diaminodiphenylsulfone (4,4′-DDS), 3,3′-diaminodiphenyl sulfone (3,3′-DDS),1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene(134APB), or 1,4-bis(4-aminophenoxy)benzene (144APB). In one embodiment,the polyimide precursor may comprise one or more or two or more of thediamines represented by the structure of Chemical Formula 2 withoutlimitation.

The polyimide precursor, the polyimide, or the combination thereofaccording to one embodiment comprises the unit comprising the structureof Chemical Formula 1, and also further comprises the unit derived fromthe diamine represented by Chemical Formula 2, whereby the polyimidefilm manufactured therefrom is colorless and transparent, residualstress occurring between glass substrates is low, and high adhesion,high mechanical properties, and an appropriate glass transitiontemperature of about 100° C. to 180° C. may be retained.

In one embodiment, the polyimide precursor, the polyimide, or thecombination thereof may further comprise a unit derived from afluorine-based diamine. The fluorine-based diamine refers to a diaminecomprising a fluorine atom. An example of the fluorine-based diamine maycomprise 2,2′-bis(trifluoromethyl)benzidine (TFMB),2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP),2,2-bis(4-aminophenyl)hexafluoropropane (BAHF),2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenylether,4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, or1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, and the like.

Besides, the polyimide precursor, the polyimide precursor, or thecombination thereof may further comprise a unit derived from the diaminecommonly used in the art disclosed in the present specification. Forexample, the unit derived from a diamine may comprise a unit derivedfrom an aromatic diamine, the aromatic diamine may be a diaminecomprising at least one aromatic ring, and the aromatic ring may be asingle ring, a fused ring of two or more aromatic rings, or a non-fusedring in which two or more aromatic rings are linked by a single bond, asubstituted or unsubstituted C₁₋₅ alkylene group, O, or C(═O). Forexample, it may further comprise a unit derived from2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (6FAP),p-phenylenediamine (pPDA), m-phenylenediamine (mPDA),p-methylenedianiline (pMDA), or m-methylenedianiline (mMDA).

In one embodiment, the polyimide precursor, the polyimide, or thecombination thereof may comprise a unit derived from an acid anhydridecommonly used in the art. For example, the acid anhydride may be an acidanhydride comprising an aromatic ring, an acid anhydride comprising analiphatic ring, a tetracarboxylic acid dianhydride, or a combinationthereof. In one embodiment, the acid anhydride may be one or more acidanhydrides selected from the group consisting of ethylene glycolbis(4-trimellitate anhydride) (TMEG-100), 4,4′-oxydiphthalic anhydride(ODPA), 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane,4,4′-(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride), pyromelliticdianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride(BPDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA),3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA),4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA),3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA),2,2-bis-(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA),p-phenylenebis(trimellitate anhydride) (TMHQ),2,2-bis(4-hydroxyphenyl)propanedibenzoate-3,3′,4,4′-tetracarboxylicdianhydride(ESDA), naphthalenetetracarboxylic dianhydride (NTDA), and derivativesthereof.

For example, the acid anhydride may be a compound represented by thefollowing Chemical Formula 4 or 5:

-   -   wherein    -   X¹ is independently of each other a C₃₋₁₀ aliphatic ring or a        C₄₋₁₀ aromatic ring, and Y¹ is a linker comprising a single        bond, a substituted or unsubstituted C₁₋₂₀ aliphatic chain, a        substituted or unsubstituted C₃₋₁₀ aliphatic ring and/or a        substituted or unsubstituted C₄₋₁₀ aromatic ring, and        specifically, Y¹ may comprise two or more C₄₋₁₀ arylene linked        by C₁₋₂₀ alkylene, C₁₋₁₀ alkylene, C₁₋₅ alkylene, C₃₋₁₀        cycloalkylene, C₄₋₁₀ arylene, two or more C₃₋₁₀ cycloalkylenes        linked by C₁₋₂₀ alkylene, or two or more C₄₋₁₀ arylene linked by        C₁₋₂₀ alkylene,

-   -   wherein    -   X² is independently of each other a C₃₋₁₀ aliphatic ring or a        C₄₋₁₀ aromatic ring, and Y² is a linker comprising a single        bond, a substituted or unsubstituted C₁₋₂₀ aliphatic chain, a        substituted or unsubstituted C₃₋₁₀ an aliphatic ring and/or a        substituted or unsubstituted C₄₋₁₀ aromatic ring, and        specifically, Y² may comprise C₁₋₂₀ alkylene, C₁₋₁₀ alkylene,        C₁₋₅ alkylene, C₃₋₁₀ cycloalkylene, C₄₋₁₀ arylene, two or more        C₃₋₁₀ cycloalkylenes linked by C₁₋₂₀ alkylene, or two or more        C₄₋₁₀ arylene linked by C₁₋₂₀ alkylene.

Specifically, the acid anhydride may be any one or more of the compoundgroups represented by the following chemical formulae:

In one embodiment, the acid anhydride may be comprised at about 30 mol %to 70 mol %, 40 mol % to 60 mol %, 45 mol % to 55 mol %, or about 50 mol%, based on the total moles of the monomer of the polyimide precursor.Otherwise, the acid anhydride may be comprised at 20 wt % to 70 wt %, 20wt % to 60 wt %, 30 wt % to 60 wt %, 20 wt % to 50 wt %, 30 wt % to 50wt %, or about 40 wt %, based on the total weight of the polyimideprecursor, but is not necessarily limited thereto.

The inorganic particles according to one embodiment may be inorganicnanoparticles, and may have an average diameter of, for example, 5 nm to50 nm, or 5 nm to 30 nm, or 5 nm to 20 nm, but is not necessarilylimited thereto.

The average diameter may be measured by, for example, observingparticles by an optical microscope, or using scanning electronmicroscope (SEM), transmission electron microscope (TEM), scanning probemicroscope (SPM), scanning tunneling microscope (STM), atomic forcemicroscope (AFM), using a particle size analyzer. For example, it may beobtained by irradiating a composition comprising inorganic particleswith laser using a laser particle size analyzer and inferring a particlesize from a correlation between diffraction and a particle size. Forexample, it may be D50, D10, or D90 value. Otherwise, for example, itmay be an area average (Ma), a number average (Mn), or a volume average(Mv) value.

In one embodiment, the inorganic particles may comprise silica,zirconium oxide, titanium oxide, zinc oxide, zinc sulfide, chromiumoxide, barium titanate, or a combination thereof. The inorganicparticles may be mixed with the polyimide resin in the form of beingdispersed in an organic solvent, or may be a surface-treated materialfor improving dispersity. For example, the inorganic particles accordingto one embodiment may have a surface substituted with a C₁₋₅ alkoxygroup, and specifically, for example, substituted with a methoxy groupor an ethoxy group. Meanwhile, the surface treatment may be performed byadopting a known surface treatment method without limitation, and thus,is not particularly limited.

In one embodiment, the inorganic particles may be chemically bonded to asubstituent of the compound represented by Chemical Formula 1. Also, thepolyimide precursor composition according to one embodiment comprisesthe inorganic particles, thereby improving a decrease in surfacehardness of a conventional shatterproof layer significantly excellently.Therefore, the shatterproof layer formed from the polyimide precursorcomposition according to one embodiment comprises the unit representedby Chemical Formula 1, thereby increasing flexibility to relax a thermalexpansion-shrinkage behavior and minimizing substrate bending therefrom,and also comprises inorganic particles to improve surface hardnessexcellently.

In one embodiment, the inorganic particles may be comprised at 1 wt % to30 wt %, 2 wt % to 25 wt %, 5 wt % to 20 wt %, or 1 wt % to 25 wt %,with respect to the total weight of the polyimide precursor composition,but is not necessarily limited to the range.

In one embodiment, a solid content of the polyimide precursorcomposition may be 40 wt % or less, 10 wt % to 40 wt %, 35 wt % or less,30 wt % or less, or 20 wt % to 40 wt %, based on the total weight of thepolyimide precursor composition. Herein, the solid content may be apolyamic acid and/or a polyimide.

In one embodiment, the polyimide precursor and/or the polyimide may havea molecular weight of 500 g/mol to 200,000 g/mol or 10,000 g/mol to100,000 g/mol, and is not necessarily limited thereto.

In one embodiment, the polyimide precursor composition may furthercomprise any one or more of pigments and dyes of blue series.

A maximum absorption wavelength of the pigments or the dyes of blueseries is not particularly limited as long as it is in a rangecomprising a yellow series wavelength range, but, for example, may be520 nm to 680 nm, 520 nm to 650 nm, 550 nm to 650 nm, or 550 nm to 620nm. By using the pigment or dyes having the maximum absorptionwavelength in the range described above, the light absorption phenomenonin the blue or violet wavelength of the polyimide film manufactured fromthe polyimide precursor composition according to one embodiment may beeffectively offset and the yellow index may be improved moreeffectively. Furthermore, by appropriately selecting the maximumabsorption wavelength range of the inorganic pigment depending on thetype and the composition of monomers used in the preparation of thepolyimide precursor composition, or the optical properties of thepolyimide film, even the optical properties such as a yellow index, arefractive index, and a retardation in the thickness direction of thefilm may be made better.

The pigment may be used without a particular limitation as long as it isa blue series pigment or a known pigment having a maximum absorptionwavelength of 520 nm to 680 nm, and for example, may be an inorganicpigment comprising natural minerals; or one or more metal selected fromzinc, titanium, lead, iron, copper, chromium, cobalt, molybdenum,manganese, and aluminum, or metal oxides thereof. The pigment may beused by being comprised in a pigment dispersion with a dispersing agent.

The inorganic pigment may have an average particle size of nm to 100 nm.Otherwise, the average particle size may be, for example, 50 nm to 100nm or 70 nm to 100 nm, but is not necessarily limited thereto. Theaverage particle size of the inorganic pigment may be, for example,measured in the dispersion or measured in the polyimide film. Also, forexample, the solid phase average particle size before dispersing thepigment may be, for example, nm to 70 nm, for example, 30 nm to 70 nm,or 50 nm to 70 nm.

A means such as ultrasonic waves may be used in the pigment forimproving dispersibility, and a dispersing agent may be used. Thedispersing agent is not particularly limited as long as it may preventagglomeration between pigments and improve dispersibility and dispersionstability of the pigment, but for example, may have a functional grouphaving high affinity to a functional group adsorbed to the pigment and adispersion medium (the organic solvent), and may be determined byadjusting a balance between the two functional groups. As the dispersingagent, various types may be used depending on the surface state of thepigment which is a subject to be dispersed. For example, the pigmentdispersing agent according to one embodiment may have an acidicfunctional group, and in this case, the acidic functional group may beadsorbed to the pigment. The acidic functional group may be, forexample, a carboxylic acid.

The dye may be a blue series dye, or a known dye having a maximumabsorption wavelength of 520 nm to 680 nm without a particularlimitation, and for example, may comprise an acidic dye, a direct dye, amordant dye, and the like. As a chemical structure, an azo-based dye, acyanine-based dye, a triphenylmethane-based dye, a phthalocyanine-baseddye, an anthraquinone-based dye, a naphthoquinone-based dye, aquinoneimine-based dye, a methine-based dye, an azomethine-based dye, asquarylium-based dye, an acridine-based dyes, a styryl-based dye, acoumarin-based dye, a quinoline-based dye, a nitro-based dye, anindigo-based dye, and the like may be comprised.

In one embodiment, the pigment may be comprised at 10 ppm to 1,500 ppm,or, for example, 100 ppm to 1,500 ppm or 500 ppm to 1,500 ppm, based onthe solid content of the polyamic acid and/or the polyimide comprised inthe polyimide precursor composition. Herein, the solid content of thepolyamic acid and/or the polyimide may refer to a polyamic acid and/or apolyimide.

In one embodiment, the dye may be comprised at 10 ppm to 500 ppm, or,for example, 10 ppm to 300 ppm, 10 ppm to 200, 50 ppm to 200 ppm, or 80ppm to 200 ppm, based on the solid content of the polyamic acid and/orthe polyimide comprised in the polyimide precursor composition. Herein,the solid content of the polyamic acid and/or the polyimide may refer toa polyamic acid and/or a polyimide.

In one embodiment, the polyimide precursor composition may furthercomprise an additive commonly used in the art disclosed in the presentspecification, and for example, may further comprise a flame retardant,an adhesive strength improver, an antioxidant, a UV protection agent, ora plasticizer.

In one embodiment, the substrate may be an ultrathin tempered glass(ultrathin glass, UTG). Otherwise, the substrate may be manufacturedfrom, for example, polyester-based resins such as polyethyleneterephthalate, polyethylene isophthalate, and polybutyleneterephthalate; cellulose-based resins such as diacetyl cellulose andtriacetyl cellulose; polycarbonate-based resins; acrylic resins such aspolymethyl (meth)acrylate and polyethyl (meth)acrylate; styrene-basedresins such as a polystyrene acrylonitrile-styrene copolymer;polyolefin-based resin having a polyethylene, polypropylene, cyclo-basedor norbornene structure, polyolefin-based resins such as anethylenepropylene copolymer; polyimide-based resins; polyamide-basedresins; polyethersulfone-based resins; sulfone-based resins, and thelike, and these resins may be used alone or in combination of two ormore.

In one embodiment, the thickness of the substrate is not particularlylimited, and for example, may be 1 μm to 50 μm, 5 μm to 50 μm, 10 μm to50 μm, 10 μm to 40 μm, 20 μm to 50 μm, 20 μm to 40 μm, or 25 μm to 35μm.

The term “front surface” used in the present specification may refer toa surface in a direction closer to the user in a lamination structure ofthe multilayer structure. On the contrary, the term “back surface” mayrefer to a surface in a direction farther from the user in a laminationstructure of the multilayer structure. In the lamination structureaccording to one embodiment, a display element may be disposed on thebackmost surface.

In one embodiment, the shatterproof layer may be formed on only any onesurface (for example, formed on a rear surface or a back surface of thesubstrate) or a front surface and a back surface (both surfaces) of thesubstrate (FIG. 2 ).

In one embodiment, when the shatterproof layer is formed on any onesurface of the substrate, the shatterproof layer may be formed on onesurface (for example, a back surface or a rear surface) of thesubstrate, and for example, may be formed in contact with one surface ofthe substrate. In addition, a hard coating layer is formed on the othersurface of the substrate on which the shatterproof layer is not formed,and, for example, may be formed on the other surface of the substrate(rear surface lamination). In addition, a display element may bedisposed on one surface (for example, the other surface not in contactwith the substrate) of the shatterproof layer.

In one embodiment, when the shatterproof layers are formed on bothsurfaces of the substrate, the optical multilayer structure may be inthe form of further comprising the shatterproof layer between thesubstrate and the hard coating layer in the case of the rear surfacelamination.

In this case, the shatterproof layers may be formed, for example, incontact with both surfaces of the substrate. A hard coating layer isformed on any one (for example, a front surface) of the shatterprooflayers formed on both surfaces of the substrate. In addition, a displayelement is disposed on the other surface of the shatterproof layer onwhich the hard coating layer is not formed.

In the optical multilayer structure according to one embodiment, theshatterproof layer is formed on any one surface of the substrate and thehard coating layer is formed on the other surface of the substrate (rearlamination, FIG. 1 ), whereby curling and a decrease in surface hardnessmay be improved excellently as compared with an optical multilayerstructure in which the shatterproof layer is formed on any one surfaceof the substrate and the hard coating layer is formed on theshatterproof layer (one side lamination).

In the optical multilayer structure according to one embodiment, theshatterproof layers are formed on both surfaces of the substrate and thehard coating layer is formed on the shatterproof layer formed (any onelayer or one or more layers of the two shatterproof layers), wherebycurling and a decrease in surface hardness may be improved excellentlyas compared with an optical multilayer structure in which theshatterproof layer is formed on any one surface of the substrate and thehard coating layer is formed on the shatterproof layer (one sidelamination).

The optical multilayer structure according to one embodiment comprises apolyimide formed from the polyimide precursor composition, therebyminimizing substrate bending and a decrease in surface hardness by aninteraction between the hard coating layer and the substratesimultaneously with enhancement of shattering resistant properties.

In one embodiment, the shatterproof layer may have a thickness of,without a particular limitation, for example, 1 μm to 100 μm, 1 μm to 80μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, or 5 μm to 15 μm, butis not necessarily limited thereto.

In one embodiment, the hard coating layer may be formed by curing acomposition for forming a hard coating layer, and also, may be acomposite hard coating layer obtained by photocuring and then thermallycuring the composition for forming a hard coating layer.

In one embodiment, the hard coating layer may be formed by comprising acondensate of alkoxysilane having an epoxy group, and for example, thecondensate of alkoxysilane having an epoxy group may be a siloxane-basedresin comprising an epoxy group, but the present disclosure is notnecessarily limited thereto. The condensate of alkoxysilane having anepoxy group may have excellent hardness and low bending properties whencured.

The epoxy group may be any one or more selected from a cyclic epoxygroup, an aliphatic epoxy group, and an aromatic epoxy group, and thesiloxane resin may refer to a polymer compound in which a silicon atomand an oxygen atom form a covalent bond.

In one embodiment, the condensate of alkoxysilane having an epoxy groupmay be a silsesquioxane resin having an epoxy group, and specifically, asilsesquioxane resin in which a silicon atom is directly substitutedwith an epoxy group or a substituent of the silicon atom is substitutedwith an epoxy group, and more specifically, the condensate ofalkoxysilane having an epoxy group may be a silsesquioxane resinsubstituted with 2-(3,4-epoxycyclohexyl)ethyl group, but is notnecessarily limited thereto.

In one embodiment, the condensate of alkoxysilane having an epoxy groupmay have a weight average molecular weight of 1,000 g/mol to 20,000g/mol, 1,000 g/mol to 18,000 g/mol, or 2,000 g/mol to 15,000 g/mol. Whenthe weight average molecular weight is in the range described above,flowability, coatability, curing reactivity, and the like of thecomposition for forming a hard coating layer may be further improved.

In one embodiment, the siloxane-based compound having an epoxy group maycomprise a repeating unit derived from an alkoxysilane compoundrepresented by the following Chemical Formula 6:

R⁶¹ _(n)Si(OR⁶²)_(4-n)  [Chemical Formula 6]

-   -   wherein R⁶¹ is a straight-chain or branched-chain alkyl group        having 1 to 6 carbon atoms substituted with an epoxycycloalkyl        group having 3 to 6 carbon atoms or an oxiranyl group, in which        the alkyl group may comprise an ether group, R⁶² is a        straight-chain or branched-chain alkyl group having 1 to 7        carbon atoms, and n is an integer of 1 to 3.

The alkoxysilane compound represented by Chemical Formula 6 may be, forexample, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,2-(3,4-epoxycyclohexyl)ethyltriethoxysilane,3-glycidoxypropyltrimethoxysilane, and the like and may be used alone orin combination of two or more, but is not necessarily limited thereto.

In one embodiment, the condensate of alkoxysilane having an epoxy groupmay be comprised at 20 wt % to 70 wt % or 20 wt % to 50 wt % withrespect to the weight of the composition for forming a hard coatinglayer, but is not necessarily limited thereof.

In one embodiment, the composition for forming a hard coating layer mayhave excellent flowability and coatability, may be uniformly curedduring the curing of the composition for forming a hard coating layer toallow effective prevention of physical defects such as cracks byovercuring, and may show excellent hardness.

In one embodiment, the hard coating layer may have a thickness of 1 μmto 100 μm, 1 μm to 80 μm, 1 μm to 50 μm, 1 μm to 30 μm, 1 μm to 20 μm,or 3 μm to 15 μm, but is not necessarily limited thereto.

In one embodiment, the optical multilayer structure may further comprisean adhesion promoting layer, an antistatic layer, an anti-fingerprintlayer, an anti-scratch layer, a low refractive index layer, a lowreflection layer, a water repellent layer, an anti-reflection layer,and/or a shock absorption layer, and the like.

The optical multilayer structure according to one embodiment comprises:

-   -   a structure in which a shatterproof layer formed by the        composition for forming a polyimide shatterproof layer (or a        polyimide precursor composition) according to one embodiment is        formed on one surface of a substrate and a hard coating layer is        formed on the other surface on which the shatterproof layer is        not formed; or    -   a structure in which the shatterproof layers are formed on both        surfaces of the substrate and the hard coating layer is formed        on any one of the shatterproof layers formed (for example, on        the shatterproof layer on the front surface), thereby having        excellent surface hardness.

The optical multilayer structure according to one embodiment may have asurface hardness of 1H or more. Otherwise, the surface hardness may be,for example, 5H or less, 4H or less, 2H or more, to 5H, 1H to 4H, 1H to3H, or 2H to 3H. The surface hardness may be an outermost surfacehardness of the optical multilayer structure, or a surface hardness ofthe shatterproof layer and/or the hard coating layer forming the opticalmultilayer structure. In one embodiment, the surface hardness may bemeasured by applying a load of a weight of 750 g using a pencil hardnesstester, and specifically, may be measured by 10 mm by setting an angleof a pencil and a specimen of about 45° at a speed of 20 mm/min. Herein,the measurement is performed three times per one specimen, and theaverage surface hardness value may be indicated. In addition, when thenumber of scratches on the specimen is two or more, it is determined tobe poor, but the surface hardness value may refer to a value beforebeing poor.

A structure in which a shatterproof layer formed by the composition forforming a polyimide shatterproof layer (or a polyimide precursorcomposition) according to one embodiment is formed on one surface of asubstrate and a hard coating layer is formed on the other surface onwhich the shatterproof layer is not formed is comprised; or

-   -   a structure in which the shatterproof layers are formed on both        surfaces of the substrate and the hard coating layer is formed        on any one of the shatterproof layers formed (for example, on        the shatterproof layer on the front surface) is comprised,        thereby improving substrate bending excellently. In one        embodiment, when a curl amount is calculated by measuring        heights of both ends of the multilayer structure or the        substrate (for example, an ultrathin glass substrate) coated        with the shatterproof layer from the ground using a ruler (or an        average of the values measured, respectively, at both ends is        calculated), the value may be 3.0 mm or less, 2.0 mm or less,        1.0 mm or less, 0.5 mm or less, 0.01 mm to 3.0 mm, 0.01 mm to        2.0 mm, 0.01 to 1.0 mm, 0.05 to 0.5 mm, 0.05 mm to 0.2 mm, or        about 0.1 mm, but is not necessarily limited thereto.

One implementation provides a method of manufacturing an opticalmultilayer structure in which a shatterproof layer is laminated on therear surface.

Specifically, the manufacturing method comprises: applying a compositionfor forming a shatterproof layer comprising a polyimide precursorcomposition comprising a polyimide precursor comprising a unit derivedfrom an acid anhydride or a diamine comprising the structure of ChemicalFormula 1, and inorganic particles and drying the composition to form ashatterproof layer; and applying a composition for forming a hardcoating layer on the other surface of the substrate and curing thecomposition to form a hard coating layer.

Another implementation provides a method of manufacturing an opticalmultilayer structure in which shatterproof layers are laminated on bothsurfaces.

Specifically, the manufacturing method comprises: applying a polyimideprecursor composition comprising a unit derived from an acid anhydrideor a diamine comprising the structure of Chemical Formula 1 on bothsurfaces of the substrate(the one surface of the substrate and the othersurface of the substrate) and drying the composition to formshatterproof layers; and applying a composition for forming a hardcoating layer on any one of the first shatterproof layer or the secondshatterproof layer formed on both surfaces of the substrate and curingthe composition to form a hard coating layer.

Herein, the polyimide precursor composition according to one embodimentmay identically apply to the polyimide precursor composition.

In one embodiment, the shatterproof layer may be formed by applying thecomposition for forming a shatterproof layer and drying the composition,and the drying may comprise, for example, two drying steps. For example,the drying may comprise first drying at a temperature of about 30° C. to60° C., 40° C. to 60° C., or 45° C. to 55° C. for about 30 seconds to120 seconds, 30 seconds to 90 seconds, or 50 seconds to 80 seconds, andthen second drying at a temperature of about 150° C. to 300° C., 180° C.to 280° C., 200° C. to 280° C., or 200° C. to 250° C. for about 1 minuteto 30 minutes, 1 minute to 20 minutes, 5 minutes to 20 minutes, or 5minutes to 14 minutes.

In one embodiment, the hard coating layer may be formed by furthercomprising a crosslinking agent having a polyfunctional epoxy group.Herein, the crosslinking agent may comprise a compound having analicyclic epoxy group, and for example, the crosslinking agent maycomprise a compound having two 3,4-epoxycyclohexyl group bonded, but isnot necessarily limited thereto. The crosslinking agent may have astructure and properties similar to the condensate of alkoxysilanehaving an epoxy group, and in this case, may promote crosslinking of thecondensate of alkoxysilane having an epoxy group.

In one embodiment, the hard coating layer may be formed by furthercomprising a thermal initiator and/or a photoinitiator.

In one embodiment, when a thermal initiator is used in the hard coatinglayer, a cure half-life may be shortened and thermal curing may berapidly performed even in low-temperature conditions, and thus, damageand deformation due to a long-term heat treatment under high-temperatureconditions may be prevented. The thermal initiator may promote thecrosslinking reaction of the epoxy siloxane resin or the crosslinkingagent when heat is applied to the composition for forming a hard coatinglayer. As the thermal initiator, a cationic thermal initiator may beused, but the present disclosure is not necessarily limited thereto.

In addition, when forming the hard coating layer, the thermal curingusing a thermal initiator and the photocuring using a photoinitiator areused in combination, thereby improving the curing degree, the hardness,the flexibility, and the like of the hard coating layer. For example,the composition for forming a hard coating layer is applied to asubstrate or the like and irradiated with ultraviolet rays (photocuring)to at least partially cure the composition, and then heat is furtherapplied (thermal curing), thereby performing substantially completecuring.

The composition for forming a hard coating layer may be semi-cured orpartially cured by the photocuring, and the composition for forming ahard coating layer which has been semi-cured or partially cured may besubstantially completely cured by the thermal curing. For example, whenthe composition for forming a hard coating layer is cured only by thephotocuring, a curing time may be excessively extended or curing may notbe completely performed in some parts. However, when the photocuring isfollowed by the thermal curing, the portion which is not cured by thephotocuring may be substantially completely cured by the thermal curing,and the curing time may be also reduced.

In addition, generally, a portion which has been already appropriatelycured is provided with excessive energy due to an increased curing time(for example, an increased light exposure time), which may causeovercuring. When the overcuring proceeds, the hard coating layer losesflexibility or mechanical defects such as curls or cracks may occur.However, the photocuring and the thermal curing are used in combination,the composition for forming a hard coating layer may be substantiallycompletely cured within a short time and the hardness of the hardcoating layer may be further improved while the flexibility of the hardcoating layer is maintained.

Though the method of first photocuring and then further thermally curingthe composition for forming a hard coating layer has been describedabove, the sequence of the photocuring and the thermal curing is notparticularly limited thereto. That is, in some embodiments, the thermalcuring may be first performed and then the photocuring may be performed,of course.

In one embodiment, the thermal initiator may be comprised at 0.1 partsby weight to 20 parts by weight or 1 part by weight to 20 parts byweight with respect to 100 parts by weight of the condensate ofalkoxysilane having an epoxy group, but is not necessarily limitedthereto. In addition, for example, the thermal initiator may becomprised at 0.01 parts by weight to 15 parts by weight, 0.1 parts byweight to 15 parts by weight, or 0.3 parts by weight to 10 parts byweight with respect to a total of 100 parts by weight of the compositionfor forming a hard coating layer, but is not necessarily limitedthereto.

In one embodiment, the photoinitiator may comprise a photocationicinitiator. The photocationic initiator may initiate polymerization ofthe epoxy siloxane resin and an epoxy-based monomer. As thephoto-cationic initiator, an iodonium salt, an onium salt and/or anorganic metal salt, and the like may be used, and for example, adiaryliodonium salt, a triarylsulfonium salt, an aryldiazonium salt, aniron-arene composite, and the like may be used alone or in combinationof two or more, but the present disclosure is not necessarily limitedthereto.

The content of the photoinitiator is not particularly limited, but forexample, the photoinitiator may be comprised at 0.1 parts by weight to15 parts by weight or 1 part by weight to 15 parts by weight withrespect to 100 parts by weight of the condensate of alkoxysilane havingan epoxy group, but is not necessarily limited thereto.

In addition, for example, the photoinitiator may be comprised at 0.01parts by weight to 10 parts by weight, 0.1 parts by weight to 10 partsby weight, or 0.3 parts by weight to 5 parts by weight with respect to atotal of 100 parts by weight of the composition for forming a hardcoating layer, but is not necessarily limited thereto.

In one embodiment, the composition for forming a hard coating layer mayfurther comprise a solvent. The solvent is not particularly limited andmay be a solvent known in the art.

A non-limiting example of the solvent may comprise alcohol-basedsolvents (such as methanol, ethanol, isopropanol, butanol, methylcellosolve, and ethyl cellosolve), ketone-based solvents (such as methylethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethylketone, dipropyl ketone, and cyclohexanone), hexane-based solvents (suchas hexane, heptane, and octane), benzene-based solvents (such asbenzene, toluene, and xylene), and the like. These may be used alone orin combination of two or more.

In one embodiment, the composition for forming a hard coating layer mayfurther comprise an inorganic filler. The inorganic filler may furtherimprove the hardness of the hard coating layer.

The inorganic filler is not particularly limited, and an example thereofmay comprise metal oxides such as silica, alumina, and titanium oxide;hydroxides such as aluminum hydroxide, magnesium hydroxide, andpotassium hydroxide; metal particles such as gold, silver, bronze,nickel, and alloys thereof; conductive particles such as carbon, carbonnanotubes, and fullerene; glass; ceramic; and the like, or in terms ofcompatibility with other components of the composition for forming ahard coating layer, silica may be used, and these may be used alone orin combination of two or more, but the present disclosure is notnecessarily limited thereto.

In one embodiment, the composition for forming a hard coating layer mayfurther comprise a lubricant. The lubricant may further improve windingefficiency, blocking resistance, wear resistance, scratch resistance,and the like.

The type of lubricant is not particularly limited, and for example,waxes such as polyethylene wax, paraffin wax, synthetic wax, or montanwax; synthetic resins such as silicon-based resins and fluorine-basedresins; and the like may be used, and these may be used alone or incombination of two or more, but the present disclosure is notnecessarily limited thereto.

Besides, the composition for forming a hard coating layer may furthercomprise additives such as, for example, an antioxidant, a UV absorber,a photostabilizer, a thermal polymerization inhibitor, a leveling agent,a surfactant, a lubricant, and an antifouling agent.

In one embodiment, the application may be performed by a die coater, anair knife, a reverse roll, a spray, a blade, casting, gravure, spincoating and the like, but is not necessarily limited thereto.

One implementation provides a window cover film comprising the opticalmultilayer structure according to one embodiment, and a flexible displaypanel or a flexible display device comprising the window cover film.

Since the multilayer structure according to one embodiment may haveminimized curling and high surface hardness, it may be effectivelyapplied to the window cover film and/or the flexible display panel.

The window cover film may be used as an outermost window substrate of aflexible display device. The flexible display device may be variousimage display devices such as a common liquid crystal display device, anelectroluminescent display device, a plasma display device, and a fieldemission display device.

Hereinafter, the examples and the experimental examples will beillustrated in detail. However, the examples and the experimentalexamples described later only illustrate a part of one implementation,and the technology described in the present specification is notconstrued as being limited thereto.

Example 1

1-1. Preparation of Composition for Forming Shatterproof Layer

An agitator with a nitrogen airflow flowing was filled with 230 g of amixed solvent of propylene glycol methyl ether (PGME) and cyclohexanone(CHN) at a mass ratio of 8:2. In a state of maintaining the temperatureof the reactor at 25° C., 29.0 g of 2,2′-bis(trifluoromethyl)benzidine(TFMB) and 29.6 g of a dimethylsiloxane-diphenylsiloxane (DMS-DPS)oligomer diamine compound (Shin-etsu, X-22-1660B-3, molecular weight:4,400 g/mol) were added thereto and dissolved. 40.0 g of ethylene glycolbis(4-trimellitate anhydride (TMEG-100) was added thereto and stirringwas performed while it was dissolved at 50° C. for 8 hours and at roomtemperature for 24 hours, thereby preparing a polyamic acid resin. Atthis time, each monomer had a mole ratio of(TFMB+X-22-1660B-3):TMEG-100=0.99:1.0. Next, silica nanoparticles(diameter: 15 nm) which were dispersed at 30 wt % inN,N-dimethylpropanamide (DMPA) were added at 5 wt % of the total weightof the composition, and stirring was performed for 3 hours, therebypreparing a composition for forming a polyimide-shatterproof layerhaving a solid content of 23 wt %.

1-2. Preparation of Composition for Forming Hard Coating Layer

2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane (ECTMS, available from TCI)and water were mixed at a ratio of 24.64 g:2.70 g (0.1 mol:0.15 mol) toprepare a mixture, which was added to a 250 mL 2-neck flask. To themixture, 0.1 mL of tetramethylammoniumhydroxide (TMAH, available fromAldrich) as a catalyst and 100 mL of tetrahydrofuran (THF, availablefrom Aldrich) were added, and stirring was performed at 25° C. for 36hours. Thereafter, layer separation was performed, a product layer wasextracted with methylene chloride (Aldrich), moisture was removed fromthe extract with MgSO₄, and the solvent was dried under vacuum to obtainan epoxy siloxane-based resin.

30 g of the epoxy siloxane-based resin prepared as described above, 10 gof (3′,4′-epoxycyclohexyl)methyl 3,4-epoxycyclohexanecarboxylate and 5 gof bis[(3,4-epoxycyclohexyl)methyl] adipate as a crosslinking agent, 0.5g of(4-methylphenyl)[4-(2-methylpropyl)phenyl]iodoniumhexafluorophosphate asa photoinitiator, and 54.5 g of methyl ethyl ketone were mixed toprepare a composition for forming a hard coating layer.

1-3. Manufacture of Optical Multilayer Structure

The composition for forming a shatterproof layer prepared above wasapplied on the back surface of a glass substrate (UTG 30 μm) with a #30Mayer bar, dried at 50° C. for 1 minute, and dried at 230° C. for 10minutes to form a polyimide shatterproof layer having a thickness of 10μm.

Next, the front surface of the glass substrate was coated with thecomposition for forming a hard coating layer prepared above with a #10Mayer bar, dried at 60° C. for 5 minutes, irradiated with UV at 1 J/cm²,and cured at 120° C. for 15 minutes to form a hard coating layer havinga thickness of 10 μm, thereby manufacturing a UTG optical multilayerstructure.

Examples 2 and 3

UTG optical multilayer structures were manufactured in the same manneras in Example 1, except that the silica nanoparticles were added at 10wt % and 20 wt %, respectively, of the total weight of the compositionin the process of preparing the composition for forming a shatterprooflayer.

Example 4

4-1. Preparation of Composition for Forming Shatterproof Layer

An agitator with a nitrogen airflow flowing was filled with 188 g ofDMPA, and 0.0058 mol of a DMS-DPS oligomer diamine compound (availablefrom Shin-etsu, X-22-1660B-3, molecular weight: 4,340 g/mol) and 0.0502mol of 1,3-bis(4-aminophenoxy)benzene (TPER) were added at the sametemperature and dissolved. 0.0561 mol of TMEG-100 was added at the sametemperature thereto, and stirring was performed at 60° C. for 4 hoursand then at room temperature for 24 hours, thereby preparing a polyamicacid resin. Next, silica nanoparticles (diameter: 15 nm) dispersed at 30wt % in DMPA were added at 5 wt % of the total weight of thecomposition, and stirring was performed for 3 hours, thereby preparing acomposition for forming a polyimide-shatterproof layer having a solidcontent of 23 wt %.

4-2. Preparation of Composition for Forming Hard Coating Layer

ECTMS and water were mixed at a ratio of 24.64 g:2.70 g (0.1 mol:0.15mol) to prepare a mixture, which was added to a 250 mL 2-neck flask. Tothe mixture, 0.1 mL of TMAH as a catalyst and 100 mL of THF were added,and stirring was performed at 25° C. for 36 hours. Thereafter, layerseparation was performed, a product layer was extracted with methylenechloride, moisture was removed from the extract with MgSO₄, and thesolvent was dried under vacuum to obtain an epoxy siloxane-based resin.

30 g of the epoxy siloxane-based resin prepared as described above, 10 gof (3′,4′-epoxycyclohexyl)methyl 3,4-epoxycyclohexanecarboxylate as acrosslinking agent, 5 g of bis[(3,4-epoxycyclohexyl)methyl] adipate, 0.5g of (4-methylphenyl)[4-(2-methylpropyl)phenyl]iodoniumhexafluorophosphate, and 54.5 g of methyl ethyl ketone weremixed to prepare a composition for forming a hard coating layer.

4-3. Manufacture of Optical Multilayer Structure

The composition for forming a shatterproof layer prepared above wasapplied on the back surface of a glass substrate (UTG 30 μm) with a #30Mayer bar, dried at 50° C. for 1 minute, and dried at 230° C. for 10minutes to form a polyimide shatterproof layer having a thickness of 10μm.

Next, the front surface of the glass substrate was coated with thecomposition for forming a hard coating layer prepared above with a #10Mayer bar, dried at 60° C. for 5 minutes, irradiated with UV at 1 J/cm²,and cured at 120° C. for 15 minutes to form a hard coating layer havinga thickness of 10 μm, thereby manufacturing a UTG optical multilayerstructure.

Examples 5 and 6

UTG optical multilayer structures were manufactured in the same manneras in Example 4, except that the silica nanoparticles were added at 10wt % and 20 wt %, respectively, of the total weight of the compositionin the process of preparing the composition for forming a shatterprooflayer.

Example 7

7-1. Preparation of Composition for Forming Shatterproof Layer

The process was performed in the same manner as in “1-1. Preparation ofcomposition for forming shatterproof layer” of Example 1.

7-2. Preparation of Composition for Forming Hard Coating Layer

The process was performed in the same manner as in “1-2. Preparation ofcomposition for forming hard coating layer” of Example 1.

7-3. Manufacture of Optical Multilayer Structure

The composition for forming a shatterproof layer prepared above wasapplied on the front surface of a glass substrate (UTG 30 μm) with a #30Mayer bar, dried at 50° C. for 1 minute, and dried at 230° C. for 10minutes to form a first polyimide shatterproof layer having a thicknessof 10 μm. Next, a second polyimide shatterproof layer having a thicknessof 10 μm was formed on the back surface of the glass substrate in thesame manner.

Next, the first polyimide shatterproof layer formed above was coatedwith the composition for forming a hard coating layer prepared abovewith a #10 Mayer bar, dried at 60° C. for 5 minutes, irradiated with UVat 1 J/cm², and cured at 120° C. for 15 minutes to form a hard coatinglayer having a thickness of 10 μm, thereby manufacturing a UTG opticalmultilayer structure.

Examples 8 and 9

UTG optical multilayer structures were manufactured in the same manneras in Example 7, except that the silica nanoparticles were added at 10wt % and 20 wt %, respectively, of the total weight of the compositionin the process of preparing the composition for forming a shatterprooflayer.

Example 10

10-1. Preparation of Composition for Forming Shatterproof Layer

The process was performed in the same manner as in “4-1. Preparation ofcomposition for forming shatterproof layer” of Example 4.

10-2. Preparation of Composition for Forming Hard Coating Layer

The process was performed in the same manner as in “4-2. Preparation ofcomposition for forming hard coating layer” of Example 4.

10-3. Manufacture of Optical Multilayer Structure

The composition for forming a shatterproof layer prepared above wasapplied on the front surface of a glass substrate (UTG 30 μm) with a #30Mayer bar, dried at 50° C. for 1 minute, and dried at 230° C. for 10minutes to form a first polyimide shatterproof layer having a thicknessof 10 μm. Next, a second polyimide shatterproof layer having a thicknessof 10 μm was formed on the back surface of the glass substrate in thesame manner.

Next, the first polyimide shatterproof layer formed above was coatedwith the composition for forming a hard coating layer prepared abovewith a #10 Mayer bar, dried at 60° C. for 5 minutes, irradiated with UVat 1 J/cm², and cured at 120° C. for 15 minutes to form a hard coatinglayer having a thickness of 10 μm, thereby manufacturing a UTG opticalmultilayer structure.

Examples 11 and 12

UTG optical multilayer structures were manufactured in the same manneras in Example 10, except that the silica nanoparticles were added at 10wt % and 20 wt %, respectively, of the total weight of the compositionin the process of preparing the composition for forming a shatterprooflayer

Comparative Example 1

A UTG optical multilayer structure was manufactured in the same manneras in Example 1, except that the silica nanoparticles were not added inthe process of preparing the composition for forming a shatterprooflayer.

Comparative Example 2

A UTG optical multilayer structure was manufactured in the same manneras in Example 4, except that the silica nanoparticles were not added inthe process of preparing the composition for forming a shatterprooflayer.

Comparative Example 3

A UTG optical multilayer structure was manufactured in the same manneras in Example 1, except that the shatterproof layer was formed on thefront surface of the substrate and the hard coating layer was formed onthe shatterproof layer, instead of forming the shatterproof layer on theback surface of the substrate and forming the hard coating layer on thefront surface of the substrate, in the step of preparing an opticalmultilayer structure.

Comparative Example 4

A UTG optical multilayer structure was manufactured in the same manneras in Example 4, except that the shatterproof layer was formed on thefront surface of the substrate and the hard coating layer was formed onthe shatterproof layer, instead of forming the shatterproof layer on theback surface of the substrate and forming the hard coating layer on thefront surface of the substrate, in the step of preparing an opticalmultilayer structure.

Comparative Example 5

A UTG optical multilayer structure was manufactured in the same manneras in Example 7, except that the silica nanoparticles were not added inthe process of preparing the composition for forming a shatterprooflayer.

Comparative Example 6

A UTG optical multilayer structure was manufactured in the same manneras in Example 10, except that the silica nanoparticles were not added inthe process of preparing the composition for forming a shatterprooflayer.

Experimental Examples

The UTG optical multilayer structures manufactured in the examples andthe comparative examples were used to measure the substrate bendingproperties and surface hardness in the following manner, and the resultsare shown in the following Table 1.

1. Measurement of Substrate Bending (Curling)

Degrees of curling from the ground of both ends of the UTG opticalmultilayer structures manufactured in the examples and the comparativeexamples were measured using a ruler, and a curl amount was calculatedas an average value of the values measured at both ends.

2. Surface Hardness Measurement

A load of a weight of 750 g was applied and a pencil hardness wasmeasured, using a pencil hardness tester (available from Ocean Science,COAD.607). An angle of a pencil (available from Mitsubishi) and aspecimen was set at 45° , and measured by 10 mm at a speed of 20 mm/min.The measurement was performed three times per one specimen, and whenthere were two or more scratches, it was determined to be poor, and thesurface hardness was indicated as a hardness before being poor.

TABLE 1 Content of inorganic Curl amount Surface particles (wt %) (mm)hardness Example 1 5 0.1 2H Example 2 10 0.1 3H Example 3 20 0.1 3HExample 4 5 0.1 2H Example 5 10 0.1 3H Example 6 20 0.1 3H Example 7 50.1 1H Example 8 10 0.1 1H Example 9 20 0.1 2H Example 10 5 0.1 1HExample 11 10 0.1 1H Example 12 20 0.1 2H Comparative Example 1 0 0.1 HBComparative Example 2 0 0.1 HB Comparative Example 3 5 0.5 1HComparative Example 4 5 0.5 1H Comparative Example 5 0 0.1 6BComparative Example 6 0 0.1 6B

As confirmed from Table 1, the UTG optical multilayer structure ofExamples 1 to 12 which comprised silica particles as inorganic particlesand had a polyimide shatterproof layer on a rear surface or bothsurfaces of the substrate had minimized curling and significantlyimproved surface hardness as compared with the comparative examples.Specifically, the examples had a significantly improved decrease insurface hardness as compared with Comparative Examples 1, 2, 5, and 6comprising no inorganic particles. In addition, the examples hadexcellently improved curling and decrease in surface hardness ascompared with Comparative Examples 3 and 4 comprising a structure inwhich the shatterproof layer was formed on the front surface of thesubstrate and the hard coating layer was formed on the shatterprooflayer.

The present disclosure relates to an optical multilayer structurecomprising a structure in which a polyimide shatterproof layer formedfrom a polyimide precursor composition comprising a polyimide precursorcomprising a siloxane structure, a polyimide, or a combination thereof,and inorganic particles is formed on any one or both surfaces of asubstrate. The optical multilayer structure according to oneimplementation is less curled to minimize substrate bending andsignificantly improve surface hardness, and thus, has excellentmechanical properties.

Hereinabove, though an exemplary embodiment has been described in detailby the preferred examples and experimental examples, the range of theembodiment is not limited to specific examples, and should be construedby the appended claims.

1. An optical multilayer structure comprising: a substrate; ashatterproof layer which is formed on one surface of the substrate andcomprises a polyimide film comprising a polyimide precursor, apolyimide, or a combination thereof comprising a structure of thefollowing Chemical Formula 1, and inorganic particles; and a hardcoating layer formed on the other surface of the substrate:

wherein R¹ and R² are independently of each other C₁₋₅ alkyl which isunsubstituted or substituted with one or more halogens; R³ and R⁴ areindependently of each other C₆₋₁₀ aryl which is unsubstituted orsubstituted with one or more halogens; L¹ and L² are independently ofeach other C₁₋₁₀ alkylene; and x and y are independently of each otheran integer of 1 or more.
 2. The optical multilayer structure of claim 1,wherein the polyimide precursor, the polyimide, or the combinationthereof further comprises a unit derived from a diamine represented bythe following Chemical Formula 2:

wherein R¹¹ and R²¹ are independently of each other hydrogen or a C₁₋₂₀monovalent organic group; L¹¹ is —SO₂—, —O—, or —C(═O)O—, or a C₁₋₂₀divalent organic group comprising any one or more of these bonds; andChemical Formula 2 does not comprise a fluorine atom.
 3. The opticalmultilayer structure of claim 1, wherein the polyimide precursor, thepolyimide, or the combination thereof further comprises a unit derivedfrom a fluorine-based diamine.
 4. The optical multilayer structure ofclaim 3, wherein the fluorine-based diamine comprises one or moreselected from the group consisting of 2,2′-bis(trifluoromethyl)benzidine(TFMB), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP),2,2-bis(4-aminophenyl)hexafluoropropane (BAHF),2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenylether,4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl,1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and mixtures thereof.5. The optical multilayer structure of claim 1, wherein R¹ and R² areindependently of each other C₁₋₃ alkyl which is unsubstituted orsubstituted with one or more halogens; R³ and R⁴ are independently ofeach other C₆₋₈ aryl which is unsubstituted or substituted with one ormore halogens; and L¹ and L² are independently of each other C₁₋₅alkylene.
 6. The optical multilayer structure of claim 1, wherein thestructure of Chemical Formula 1 is a structure of the following ChemicalFormula 3:

wherein L¹ and L² are independently of each other C₁₋₁₀ alkylene; and xand y are independently of each other an integer of 1 or more.
 7. Theoptical multilayer structure of claim 2, wherein R¹¹ and R²¹ areindependently of each other hydrogen or a C₁₋₁₀ monovalent organicgroup; and L¹¹ is —SO₂—, —O—, or —C(═O)O—, or a C₁₋₁₅ divalent organicgroup comprising any one or more of these bonds.
 8. The opticalmultilayer structure of claim 2, wherein L¹¹ is —SO₂—, —O—, or —C(═O)O—,or a combination of any one or more of —SO₂—, —O—, or —C(═O)O— and anyone or more selected from the group consisting of C₁₋₁₀ alkyl, C₅₋₁₈cycloalkylene, and C₆₋₁₈ arylene.
 9. The optical multilayer structure ofclaim 1, wherein the inorganic particles comprise silica, zirconiumoxide, titanium oxide, zinc oxide, zinc sulfide, chromium oxide, bariumtitanate, or a combination thereof.
 10. The optical multilayer structureof claim 1, wherein the hard coating layer comprises a siloxane-basedcompound comprising an epoxy group.
 11. The optical multilayer structureof claim 1, further comprising a second shatterproof layer between thehard coating layer and the other surface of the substrate.
 12. A methodof manufacturing the optical multilayer structure according to claim 1,the method comprising: applying a polyimide precursor composition on onesurface of a substrate and drying the composition to form a shatterprooflayer; and applying a composition for forming a hard coating layer onthe other surface of the substrate and curing the composition to form ahard coating layer.
 13. A method of manufacturing the optical multilayerstructure according to claim 11, the method comprising: applying apolyimide precursor composition on the one surface of the substrate andthe other surface of the substrate and drying the composition to form afirst shatterproof layer on the one surface of the substrate and asecond shatterproof layer on the other surface of the substrate; andapplying a composition for forming a hard coating layer on any one ofthe first shatterproof layer or the second shatterproof layer formed onthe substrate and curing the composition to form a hard coating layer.14. A window cover film comprising the optical multilayer structureaccording to claim
 1. 15. A flexible display panel comprising the windowcover film according to claim
 14. 16. The optical multilayer structureof claim 1, wherein the inorganic particles comprise silica.